Prior to this commit, the receiver code was assuming only
2 inputs always, when it decided how to change the input
ordering (randomly doing a reversal), but this is not correct
according to the BIP78 spec, which requires that the
receiver's inputs are *inserted* randomly, without changing
the ordering of the existing (sender) inputs. After this
commit, the BIP78 protocol is adhered to for any number of
inputs.
Added test for random_insert and for payjoin with 3 inputs
Adam Gibson
James Hilliard
undeath